About 12.6 million units (including approximately 643,000 autologous donations) of whole blood are donated in the United States each year by approximately eight million volunteer blood donors. These units are transfused to about four million patients per year. Typically, each donated unit of blood, referred to as whole blood, may be separated into multiple components, such as red blood cells, plasma, clotting factors, gamma globulin and platelets. The need for blood is great: on any given day, approximately 32,000 units of red blood cells are needed. Accident victims, people undergoing surgery and patients receiving treatment for leukemia, cancer or other diseases such as sickle cell disease and thalassemia, all utilize blood.
Because patients seldom require all of the components of whole blood, it is the usual practice in blood banks to separate the blood into components and transfuse only that portion needed by the patient for a specific condition or disease. This treatment, referred to as “blood component therapy” allows several patients to benefit from each unit of blood.
Whole blood is a living tissue that circulates through the heart, arteries, veins and capillaries, carrying nourishment, electrolytes, antibodies, heat and oxygen to the body tissues. Whole blood is comprised of red blood cells, white blood cells and platelets suspended in a proteinaceous fluid termed blood plasma. If blood is treated to prevent clotting and permitted to stand in a container, red blood cells will settle to the bottom of the container, the plasma will remain on top and the white blood cells will form a layer on top of the red blood cells. A centrifuge is commonly used to hasten this separation. The platelet-rich plasma is then removed and placed into a sterile bag for further processing to separate, for example, platelets, clotting factors, albumin, immunoglobulins and the like.
The most important component for the usual transfusion need are the erythrocytes or red blood cells (RBC), which contain hemoglobin, a complex iron-containing protein that carries oxygen throughout the body and gives blood its red color. The percentage of blood volume that is composed of red blood cells is called the “hematocrit.” The average hematocrit in the adult male is 47%. There are about one billion red blood cells in two or three drops of blood, and, for every 600 red blood cells, there are about 40 platelets and one white blood cell.
Manufactured in the bone marrow, RBCs are enucleated, biconcave discs that are continuously being produced, broken down and destroyed. The biconcave disc shape is crucial to the function of RBCs, presenting a maximal surface area for the capture of oxygen in the lungs and its release in the tissue. The cells are flexible and able to bend in order to traverse the tiny tubules of the capillary beds. Since the cells are enucleated and lack mitochondria, they are unable to carry out cellular repair of damage or enzyme inactivation and must rely on anaerobic phosphorylation for energy. After an average 120 days in the circulatory system, the cells are senescent and are phagocytized by circulating monocytes or the fixed macrophages of the reticulo-endothelial system.
Red blood cells are prepared from whole blood by removing the plasma. When transfused into a patient, the hematocrit is raised while increase in blood volume is minimized, which is especially important to such patients as those with congestive heart failure. The cells are typically suspended in about half the original volume; the preparation is referred to as packed red cells. Patients benefitting most from transfusions of packed red cells include those with chronic anemia from disorders such as kidney failure, malignancies, gastrointestinal bleeding or acute blood loss as from trauma or surgery.
Standard solutions for the storage of whole blood comprise citrate-phosphate-dextrose solution (CPD) and citrate-phosphate-dextrose-adenine solution(CPDA). Citrate or other anticoagulants such as heparin are necessary to prevent clotting. Because blood is a living tissue that maintains metabolic functions even at refrigerated temperatures, it has been considered necessary to provide an energy source such as glucose. Phosphate ion can be used to buffer the lactate produced from glucose utilization.
Improvements in cell preservation solutions over the last 15 years have increased the refrigerated shelf life of whole blood or red blood cells from 21 to 42 days. After 42 days, the blood is discarded, since many of the cells have become senescent and would be immediately phagocytized upon transfusion into a recipient. Although the red cells may appear to survive in storage for five or six weeks, they rapidly develop “storage lesion” characterized by biochemical and biomechanical changes that compromise their ability to accept, transport and unload oxygen to the tissue. For that reason, it is desirable to use the whole blood and blood products within three weeks or less of drawing.
The need remains for a solution in which blood cells in whole blood or packed red cell suspensions can be stored for an increased time and survive functionally when transfused into a recipient. The need also remains for a method to rejuvenate blood and RBCs which are suboptimally functional.